Cross linked copolymer



United States Patent I cc ,jjfiffli 2,847,406 Example 1 CROSS LINKED COPOLYMER Use the following formula:

Norman R. Legge, Buechel, Ky., assignor, by mesne as- Parts Per 100 signments, to American Synthetic Rubber Corporation, 5 lngredlemoi Parts monomer New York, N. Y., a corporation of Delaware gutadlene I tyrene 28.5 No Drawlugerl ta uglgagtillzggrch 15, 1954 V V heme? 05 ater 180.0

I Clalms' (CL Dresinate 214. 4,0 T1118 invention concerns the polymers produced by co- CHP 0.35

polymerization of butadiene and Styrene and more espe- FeSO -7H O 0.35

clally those copolymers produced by the polymerization K P O 0.42

of butadlene and styrene in the presence of divinyl ben- Sulfole 0.15

Zene. The eifects desired by use of crosslinking agents DaXad l1 0.15

are predominantly to retain a high tensile strength while w rm-1211 0 0.50

ncreasing the amount of crosslinking and thus improv- Goodrite #3955 0.15

mg mill shrinkage. Water 7.30

A great amount of research and development work The Dresinate 214 Daxad 11 d trisodium phoshas been performed in an efiort to improve the physical properties, especially tensile strength, of crosslinked cogg ffi gz gfi zi 2 5 2 fi ig g g s igg polymers of butadiene and styrene. For many normal I efi b J 2 0 operations, the crosslinked polymers may be used in z e i g g and a1f.the dlvmhjl small percentages as compounding ingredients with other if g l gfiz 3 2 i 3 3 2 3 g xg g rubbers and the drop in tensile strength below that nor- The mulsion is cooled 3 0 F At 46 conversion' mally found in the non-crosslinked rubber is not serious. the second half of the divin 1 ber'lzene. is g The When a crosslinked copolymer is used in high percent- I H d y 61 ages or alone, however the low tensile strength develac [on Is a owe to run to converslonireqmrmg oped becomes a Serious Problem Much development about 14 hours. The polymerlzatlon reaction ls stopped work has tended to indicate that variation in recipe or by addltlon of an aqueous solution of Sodlum dlmeth' yldlthlocarbamate and the copolymer is coagulated by a varlatlon 1n reactlon temperatures produces no slgnlficant 1f l hl increases in tensile strength of crosslinked polymers, so SH unc ac! aqueous so utlon C(mtammg so mm c that the present state of the art indicates that cross linking to develop desirable properties of low shrinkage and Example A (Illustrating Conventional Procedure) ablhty to smooth the appearance of compounds In this example, the formula is the same and the steps sult in a loss of tenslle strength. In general, the use of are the same except that all the divinyl benzene was more styrene, that is, an increase in styrene content of added initia11y the polymer, will result in an increase of tensile strength. The properties of the two Products that of Example 1 For example, mcreasmg the styrene content to 45% may (illustrating the i i d that of Example A (illusresult in an increase of approximately 15% in the tratin conventional rocedure are shown below sile strength, but this does not appear to be an adequate 40 g p solution. The crosslinked polymers, as mentioned before, are generally used as processing agents in calendering or shaping operations and these polymers have been Example Example 1 A found to have generally inferior properties as compared 1(\)1Z;i11llJ%1ullktGnSlleStIBn%th,p.S.l 2,350 2,250 s rl age,pereen 23.9 21.1 10 the propertles 0f GRS- I11 Partlcular, the tenslle vistex 1 1 @045 0 ()3 strength of the vulcanizate is lowered by the inclusion of the crosslinked polymers, which polymers themselves have low tensile strength.

The invention therefore is directed toward an improve- Further examples of the invention are as follows. Polymerization temperature 41 F.

ment in the properties, especially the tensile strength, of crosslinked polymers without corresponding depreciation Example Example Example of their utility as processing aids. 2 3 4 In accordance with the present invention, divinyl ben- Butadlene 64.25 64.30 04 45 zone is used as the essential crossllnklng agent. In con- 3M0 3500 35:00 trast with prior procedures this is added in increments as 0. 75 Y 0.7 4 0.68 copolymen'zation proceeds. The result is a crosslinked 398 593 398 copolymer having greatly improved tensile strength with 8.10 0.10 0.10 no substantial loss of processing characteristics. Further 1%; 81E 8}; in accordance with the invention, the butadiene and sty- 0 0.30 0. 30 rene are used in the proportion of -83% butadiene 81% 8: 3;;3 and 40-17 styrene and the divinyl benzene is used in Wingswp B Mo Q20 015 the proportion of 0.01 to 1%. The percentages ln l a Water 7.00 7. 00 7100 are by weight. The butadiene, styrene and divinyl ben- KORE Soap L00 zone are emulsified in an aqueous medium and the emul- Reaction Time, hours 15, 1 2&5 sifying agent may be a potassium rosin soap. All of the gggggggggg3$ 2 g? butadiene and styrene are added initially but the divinyl M111 Shrinkage, percent: "I: '28 '25 34 benzene is added in increments as described. The polygg 'ggg gifi g gg gp lg 3 3 merizing reaction is carried out at a temperature of 35- 45 o F- and PH of Said emulsion above In Examples 2, 3 and 4 the steps are the same as in Example 1 except The principles of the invention will be defined in the that the divinyl benzene was added in increments as shown in notes 1,

claims and illustrated by the following examples: fi g tgafg (DVB) Schedule Ex,

Conversion, percent DVB, parts added 2 Divinyl benzene Schedule Exf3: Wlth held initially. From 5 to 71% conversion, added 0.78 part at rate of 0.012 part/1% conversion.

3 Sullole Schedule Ex. 3:

Conversion, percent.

41 Sulfole, part 4 Divinyl benzene Schedule Ex. 4:

Conversion At 21.5% conversion 0.32 DVB was added. At- 45% conversion 0.36 DVB was added. The above proprietary names and abbreviations, and the corresponding chemical terms are shown in the following table:

Dresinate 214 A potassium rosin soap.

CHP C umene hydroperoxide.

Sulfole Tertiary dodeeyl mercaptan.

Daxad 11. a"- A polymerized sodium salt of an alkyl sulfonic acid. Goodrite 305a A mixture of sodium dimethyldithiocarbarnate and sodium polysulfide in water. PMHP Paramenthane hydroperoxide. Wingstop B Sodium dimethyldithiocarbamate in aqueous solution. Divinyl benzene. A potlassium soap. Oflice'of Rubber Reserve for- DVB KORR Soap 4' action period to improve the tensile strength of the rubber polymer.

2. In the batch emulsion polymerization process for producing synthetic rubber by copolymerization of butadiene and styrene in the proportions of 60% to 83% butadiene and 40% to 17% of styrene in a reaction mixture that includesdivinylbenzene as a cross-linking agent, the improvement which comprises adding the divinylbenzene to the reaction mixture continuously at a substantially uniform rate over a major part of the reaction period.

3. In the batch emulsion polymerization process for producing synthetic rubber by copolymerization of butadiene and styrene in the proportions of 60% to 83% butadiene and 40% to 17% of styrene in a reaction mixture that includes divinylbenzene as across-linl ing agent, the improvement which comprises adding the divinylbenzene to the reaction mixture in substantially equal portions at substantially spaced intervals during the course of the raction.

4. In the batch emulsion polymerization process for producing synthetic rubber by copolymerization of butadiene and styrene in the proportions of 60% to 83% butadiene and 40% to 17% of styrene in a reaction mixture that includes divinylbenzene as a crosslinking agent, the improvement which comprises adding the divinylbenzene to the reaction mixture in two approximately equal portions at times corresponding to about 20% and 45% conversion of the reactants to the copolymer.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE BATCH EMULSION POLYMERIZATION PROCESS FOR PRODUCING SYNTHETIC RUBBER BY COPOLYMERIZATION OF BUTADIENE AND STYRENE IN THE PROPORTIONS OF 60% TO 83% BUTADIENE AND 40% TO 17% OF STYRENE IN A REACTION MIXTURE THAT INCLUDES DIVINYLBENZENE AS A CROSS-LINKING AGENT, THE IMPROVEMENT WHICH COMPRISES ADDING THE DIVINYL BENZENE TO THE REACTION MIXTURE IN TWO OR MORE SEPARATE PORTIONS AT SUBSTANTIALLY SPACED INTERVALS DURING THE REACTION PERIOD TO IMPROVE THE TENSILE STRENGTH OF THE RUBBER POLYMER. 